394 



he has long thought must have been the conditions in sonoe parts 

 of the Bkie Ridge and South Mountain Chain in the Middle 

 States, and such perhaps were the influences which operated on 

 the gneissoid conglomerates of the Green Mountains, to which 

 Prof. Hitchcock has referred in his recent communication to 

 the Society. 



Prof. Rogers next made some remarks upon the group 

 of rocks constituting the base of the Paleozoic series in 

 the United States. 



He stated that the Potsdam sandstone, as exhibited in New- 

 York, forms one of a group of deposits which were long since 

 recognized, in the Virginia and Pennsylvania surveys, as forming 

 together the lowest assemblage of formations in this series. Tiiese 

 Primal rocks, as they have been named in the surveys referred 

 to, begin, where most developed, with a coarse conglomerate, fol- 

 lowed by a great mass of grits and slates, and then by the sand- 

 stone with ScoUtlios and Lingulce corresponding to the Potsdam 

 in New York, and the group terminates above with a formation 

 of argillaceous slate, which toward the southwest has great thick- 

 ness and a predominance of red coloring. 



These several members of the Primal series follow each other 

 in a perfectly conformable sequence, resting at their base, more or 

 less discordantly, on the still more ancient metamorphic schists, 

 and other rocky masses, which form the southeastern margin of 

 the Appalachian area. Although no unequivocal marks of fossils 

 have as yet been found lower in the group than the Potsdam sand- 

 stone, it is far from impossible that in the less altered portions of 

 the belt the inferior slates and sandstones of the group may dis- 

 close distinguishable traces of organized existence. 



As the Primal series here described, of which the Potsdam 

 sandstone is the chief fossiliferous representative, occupies the 

 base of the Paleozoic series in this country, and the Primordial 

 group of Barrande has a like position in Bohemia and other 

 parts of Europe, and as the two are found to agree in certain 

 paleontological features, they may be regarded as geologically 

 correspondent, although not in their details necessarily equivalent 

 or contemporaneous. 



